I won't be making it again unless someone else requests it. There's nothing wrong with the recipe, which I took from Joy of Baking; in fact the brownie base was excellent - dark, rich, fudgey and a little bitter because of the chocolate I chose to use (I used chocolate with 85% cocoa solids as I didn't have any unsweetened). I just didn't like how sweet it got with marshmallows on top - the sweetness overwhelmed everything, even the bitterness of the base, and the only thing which came through was the flavour of too sweet chocolate and the crunch of the nuts.
So it's a personal thing - I'd certainly recommend the recipe to anyone who wanted to try them, but the final result wasn't to my taste.
The only change I made was to increase the weight of chocolate chips to 120g, but I used half chocolate and half fudge chips. The nuts I used were a mix of large pieces of macadamias and finely chopped hazelnuts.
My one mistake was to leave the topped brownie in the oven a minute or two too long - my rocky road looks like melted tarmac!